The lost sunspot cycle: New support from Be10 measurements

TL;DR

This study uses Be10 measurements and Bayesian analysis to support the hypothesis of a previously unrecognized solar cycle between 1790 and 1830, which impacts understanding of solar magnetic activity.

Contribution

It provides new evidence from Be10 data supporting the existence of the 'lost' solar cycle, refining historical solar cycle chronology.

Findings

Bayesian analysis supports the existence of the lost cycle.

Be10 measurements show different cosmic ray effects consistent with an extra cycle.

Implications for understanding stellar activity cycles.

Abstract

It has been suggested that the deficit in the number of spots on the surface of the Sun between 1790 and 1830, known as the Dalton minimum, contained an extra cycle that was not identified in the original sunspot record by Wolf. Though this cycle would be shorter and weaker than the average solar cycle, it would shift the magnetic parity of the solar magnetic field of the earlier cycles. This extra cycle is sometimes referred to as the 'lost solar cycle' or 'cycle 4b'. Here we reanalyse Be10 measurements with annual resolution from the NGRIP ice core in Greenland in order to investigate if the hypothesis regarding a lost sunspot cycle is supported by these measurements. Specifically, we make use of the fact that the Galactic cosmic rays, responsible for forming Be10 in the Earth's atmosphere, are affected differently by the open solar magnetic field during even and odd solar cycles. This fact enables us to evaluate if the numbering of cycles earlier than cycle 5 is correct. For the evaluation, we use Bayesian analysis, which reveals that the lost sunspot cycle hypothesis is likely to be correct. We also discuss if this cycle 4b is a real cycle, or a phase catastrophe, and what implications this has for our understanding of stellar activity cycles in general.